【Objective】Obstacle avoidance is a crucial issue in unmanned aerial vehicle(UAV) operation. Ultrasonic transducers are critical components in UAV obstacles avoidance system. The vibration characteristics of UAV are important to increase UAV obstacles avoidance capability. Research was conducted to understand the vibration characteristics of small-size UAV(SUAV) and impacts of vibration on ultrasonic sensors. 【Method】Spatial distributions of SUAV vibration strength and the distributions in frequency domain were derived by acquiring SUAV vibration data at multiple test points with different throttles. The impact of SUAV vibration characteristic on ultrasonic transducer performance was detected through the spatial distribution of vibration strength. 【Result】With the distance away from the center and along the arms of SUAV, the increase and decrease of vibration strength occurred alternatively. Equipped with propellers, the ultrasonic transducer had a max error of 0.69 m in horizontal direction while the maximum error only reached 0.20 m in vertical direction. 【Conclusion】With the distance away from center and throttles increasing, the amplitude of vibration is strengthened. To avoid the effect of vibration, it is necessary to adjust the vibrational frequency of sensor. Findings reported in this paper may provide guidance for applications of ultrasonic transducer in agricultural SUAVs.